This invention is concerned with improvements relating to document shredding machines, particularly of the kind comprising two cutter assemblies, each assembly comprising a drive shaft upon which cutter discs are mounted at spaced intervals, the assemblies being mounted so that the discs of one assembly enter into the gaps between the discs of the other assembly with little or no clearance, the machine comprising drive means to rotate the drive shafts in opposite directions, so that the overlapping discs collectively act to cut material fed into the nip of the machine into narrow strips. Such machines are hereinafter referred to as being of the kind specified.
In the operation of machines of the kind specified, a common problem is encountered in the shredding of paper. To maximise throughput, it is desirable to feed into the nip several sheets simultaneously, which are all cut into narrow strips. However when too many sheets are fed into the nip simultaneously, the machine will jam.
When this happens, the paper may be pulled away from the nip: however this may be difficult to accomplish, especially where the machine comprises cutting discs, each of which has a plurality of angularly-spaced notches to cut the strips transversely into short lengths. Additionally, this method of unjamming requires the incorporation of safety devices, to render the drive means incapable of operation whilst the machine is being unjammed.
Thus, it has previously been suggested to provide in a machine of the kind specified a reversing means for the drive motor, so that when jamming occurs, the direction of rotation of the cutter discs may be reversed, to eject the jammed material from between the cutter discs. However the use of reversing means adds to the cost of the machine, and under certain circumstances jamming occurs which cannot be removed even by reversing the direction of drive.